Jet Jockey, exposure is a funny thing, especially on phone cameras. I suspect it wasn't as dark in the cabin as that vid makes it look, having seen the other videos of the incident shot both internally and externally. Early morning and overcast, for sure, so it wasn't bright daylight. But the human eye is (if I recall) something like a thousand times more sensitive to light than a phone camera. Just because the camera shows the scene as dark, doesn't mean the human eye would see it like that.
That said, the billowing black smoke from the starboard side would certainly have reduced the ambient light. But have a look at the images on this video
SIA flight catches fire while making emergency landing in Singapore - Channel NewsAsia - there are some better-exposed stills from inside the cabin around 00:30.
Of course I don't know what it was really like in the cabin, and I absolutely don't want to get into a pissing contest! My point is simply that we shouldn't necessarily trust phone camera footage on youtube, shot by someone under extreme duress, to give a true indication of light levels in the cabin as they were actually perceived by the human eye.